3 research outputs found
Electrochemical Treatment of the Antibiotic Sulfachloropyridazine: Kinetics, Reaction Pathways, and Toxicity Evolution
The electro-Fenton treatment of sulfachloropyridazine
(SCP), a model for sulfonamide antibiotics that are widespread in
waters, was performed using cells with a carbon-felt cathode and Pt
or boron-doped diamond (BDD) anode, aiming to present an integral
assessment of the kinetics, electrodegradation byproducts, and toxicity
evolution. H<sub>2</sub>O<sub>2</sub> electrogeneration in the presence
of Fe<sup>2+</sup> yielded <sup>ā¢</sup>OH in the solution bulk,
which acted concomitantly with <sup>ā¢</sup>OH adsorbed at the
anode (BDDĀ(<sup>ā¢</sup>OH)) to promote the oxidative degradation
of SCP (<i>k</i><sub>abs,SCP</sub> = (1.58 Ā± 0.02)
Ć 10<sup>9</sup> M<sup>ā1</sup> s<sup>ā1</sup>)
and its byproducts. A detailed scheme for the complete mineralization
was elucidated. On the basis of the action of <sup>ā¢</sup>OH
onto four different SCP sites, the pathways leading to total decontamination
includes fifteen cyclic byproducts identified by HPLC and GC-MS, five
aliphatic carboxylic acids, and a mixture of Cl<sup>ā</sup>, SO<sub>4</sub><sup>2ā</sup>, NH<sub>4</sub><sup>+</sup>,
and NO<sub>3</sub><sup>ā</sup> that accounted for 90ā100%
of initial Cl, S, and N. The time course of byproducts was satisfactorily
correlated with the toxicity profiles determined from inhibition of <i>Vibrio fischeri</i> luminescence. 3-Amino-6-chloropyridazine
and <i>p</i>-benzoquinone were responsible for the increased
toxicity during the first stages. Independent electrolyses revealed
that their toxicity trends were close to those of SCP. The formation
of the carboxylic acids involved a sharp toxicity decrease, thus ensuring
overall detoxification
Regeneration of Activated Carbon Fiber by the Electro-Fenton Process
An electro-Fenton (EF) based technology
using activated carbon
(AC) fiber as cathode and BDD as anode has been investigated for both
regeneration of AC and mineralization of organic pollutants. The large
specific surface area and low intraparticle diffusion resistance of
AC tissue resulted in high maximum adsorption capacity of phenol (PH)
(3.7 mmol g<sup>ā1</sup>) and fast adsorption kinetics. Spent
AC tissue was subsequently used as the cathode during the EF process.
After 6 h of treatment at 300 mA, 70% of PH was removed from the AC
surface. The effectiveness of the process is ascribed to (i) direct
oxidation of adsorbed PH by generated hydroxyl radicals, (ii) continuous
shift of adsorption equilibrium due to oxidation of organic compounds
in the bulk, and (iii) local pH change leading to electrostatic repulsive
interactions. Moreover, 91% of PH removed from AC was completely mineralized,
thus avoiding adsorption of degradation byproducts and accumulation
of toxic compounds such as benzoquinone. Morphological and chemical
characteristics of AC were not affected due to the effect of cathodic
polarization protection. AC tissue was successfully reused during
10 cycles of adsorption/regeneration with regeneration efficiency
ranging from 65 to 78%, in accordance with the amount of PH removed
from the AC surface
Some Theoretical and Experimental Insights on the Mechanistic Routes Leading to the Spontaneous Grafting of Gold Surfaces by Diazonium Salts
The
spontaneous grafting of diazonium salts on gold may involve
the carbocation obtained by heterolytic dediazonation and not necessarily
the radical, as usually observed on reducing surfaces. The mechanism
is addressed on the basis of DFT calculations and experiments carried
out under conditions where the carbocation and the radical are produced
selectively. The calculations indicate that the driving force of the
reaction leading from a gold cluster, used as a gold model surface,
and the carbocation to the modified cluster is higher than that of
the analogous reaction starting from the radical. The experiments
performed under conditions of heterolytic dediazonation show the formation
of thin films on the surface of gold. The grafting of a carbocation
is therefore possible, but a mechanism where the cleavage of the ArāN
bond is catalyzed by the surface of gold cannot be excluded